The present invention relates to an antenna apparatus. More specifically, the present invention relates to an antenna apparatus appropriately used for an ultra small communication module installed in various electronic devices such as personal computers, portable telephones, audio devices, etc. having an information communication capability, a data storage capability, etc.
Owing to digitization of information signals, various types of information such as audio information, image information, etc. can be easily handled on personal computers, mobile devices, etc. Audio and image codec technologies are used to promote the band compression of these types of information. The digital communication and the digital broadcasting are creating an environment to easily and efficiently deliver such information to various communication terminal devices. For example, audio video data (AV data) can be received on a portable telephone.
A system for sending and receiving data is being widely used in various places including homes in accordance with a proposal for simple communication network systems available in small areas. As a communication network system, special attention is paid to, for example, a 5 GHz band narrow-area wireless communication system proposed in the IEEE802.11a, a 2.45 GHz band wireless LAN system proposed in the IEEE802.11b, and a next-generation wireless communication system such as so-called Bluetooth and other short-range wireless communication systems.
The above-mentioned various electronic devices require interface specifications capable of connection to all communication networks. A wireless communication means is provided to even mobile electronic devices exclusively for personal use, enabling communication with various devices and systems in a mobile situation for interchanging data and the like. For connection with other devices, the mobile electronic device is provided with a wireless communication function such as a plurality of wireless communication ports, wireless communication hardware, etc. having interface functions compliant with the associated communication systems.
Digitization of AV data enables to easily record and store data on personal computer""s storage devices using recording media such as hard discs, optical discs including magnet-optical discs, semiconductor memory, etc. The recording media used for these types of storage devices are generally being used in place of recording media according to conventional analog recording systems such as audio or video tape cassettes, video discs, etc. having proprietary formats. Particularly, semiconductor memory chips such as flash memory are characterized by a very small cubic volume per recording capacity and ease of attaching or detaching from devices. For example, semiconductor memory chips are used for various electronic devices such as digital still cameras, video cameras, portable audio devices, notebook computers, etc.
The semiconductor memory chip helps easily move, record, store, etc. data such as audio or image information between the electronic devices. In order to move, transport, or store data, however, the semiconductor memory chip generally needs to be attached or detached from the device, causing a troublesome operation.
As mentioned above, a plurality of wireless communication functions are provided to various electronic devices. Generally, it is enough to use one function according to the usage condition, environment, etc. There is hardly a case of using a plurality of functions at a time. Because of a plurality of functions provided, the electronic devices have been subject to a problem of a cross talk or a radio interference with each other in the same or different frequency bands. Particularly, a mobile electronic device impairs the portability by mounting wireless communication ports, wireless communication hardware, etc. to provide wireless communication functions corresponding to the above-mentioned plurality of communication systems.
The electronic device provides the wireless communication function by attaching a wireless communication module having the storage function and the wireless communication function using semiconductor memory. This type of mobile electronic devices can comply with various communication systems and decrease the structural complexity by attaching appropriately selected wireless communication modules compliant with various communication systems.
FIGS. 1 and 2 show a configuration of wireless communication module used for a mobile electronic device. A wireless communication module 200 as shown in FIGS. 1 and 2 comprises a printed circuit board 201 where an appropriate wiring pattern is formed on one surface and a ground pattern 202 is formed on the other surface. There are mounted an RF module 203, an LSI 204 constituting a signal processing section, a flash memory element 205, a transmitter 206, etc. The wireless communication module 200 is mounted with a connector 207 for connection with the device at one end on the other surface of the printed circuit board 201. The wireless communication module 200 contains an antenna section 208 patterned at one end of the wiring pattern surface opposite the connector 207 on the printed circuit board 201.
The wireless communication module 200 is attached to or detached from the main device such as a mobile device via the connector 207 to store data and the like supplied from the main device in the flash memory element 205 and transfer data and the like stored in the flash memory element to the main device. When attached to the main device, the wireless communication module 200 uses the externally protruded antenna section 208 to enable wireless interchange of signals between the main device and a host device or a wireless system for wireless connection with the main device.
The antenna section 208 is patterned on a principal plane of the printed circuit board 201. For miniaturization of the wireless communication module 200, the antenna section 208 comprises a monopole antenna as a built-in antenna having a relatively simple structure. For example, a so-called reverse F-shaped antenna as shown in FIG. 1 is used for the antenna section 208. The reverse F-shaped antenna comprises an antenna element 209 formed along the width direction of the printed circuit board 201 at one end, an earth pattern 210, and a power supply pattern 211. The earth pattern 210 is formed orthogonally to the antenna element 209 at its one end and is short-circuited to the ground pattern 202. The power supply pattern 211 is formed parallel to the earth pattern 210, orthogonally to the antenna element 209, and is supplied with power from the RF module 203, for example. The reverse F-shaped antenna allows the main polarized wave direction to cross the antenna element 209 at the right angle.
The antenna section 208 may use not only the stick antenna element 209 formed as a pattern on the printed circuit board 201, but also a plate antenna element 215 as shown in FIG. 3. The antenna element 215 may be patterned on the principal plane of the printed circuit board 201, but also be mounted in a lifted manner from the principal plane of the printed circuit board 201 as shown in FIG. 3. At one end of the antenna element 215, there are provided an earth section 216 connected to the ground pattern 202 and a power supply point 217.
As shown in FIG. 4, the antenna section 208 may be configured as a so-called reverse L-shaped antenna by forming a power supply section 219 orthogonally to one end of the antenna element 218. The antenna section 208 may be configured to be, e.g., a loop pattern antenna, a micro-split pattern antenna, etc. as the other monopole antennas.
The wireless communication module 200 promotes miniaturization by providing the above-mentioned antenna section 208, but may greatly change antenna characteristics depending on states of attaching the module to the main device. The wireless communication module 200 is attached to or detached from various electronic devices for use. States of the electromagnetic field near the antenna element vary with the ground surface size of the main device, a case material, a dielectric constant, etc. Accordingly, the wireless communication module 200 is subject to a large change in antenna characteristics such as a resonance frequency, a band, sensitivity, etc.
To solve these problems, the wireless communication module 200 needs to mount an antenna apparatus with wideband characteristics for providing the sufficient sensitivity in an intended frequency band corresponding to characteristics of all main devices used. Basic characteristics of the antenna apparatus depend on the cubic volume. It is very difficult to configure the antenna apparatus so as to provide the sufficient wideband characteristics while maintaining the miniaturization. Therefore, the antenna apparatus has been a hindrance to miniaturization of the wireless communication module with good radio characteristics.
The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide an antenna apparatus capable of eliminating the need for adjustment independently of usage conditions, implementing wideband characteristics for good wireless communication, and achieving the miniaturization.
To achieve the above-mentioned objects, the antenna apparatus according to the present invention provides an antenna section having an antenna element provided with at least two or more power supply points and at least two or more earth points; a power supply point selection switch which is provided for each of the power supply points and connects or disconnects each power supply point from a power supply section; and an earth point switch which is provided for each of the power supply points and connects or disconnects each earth point from a ground.
In the antenna apparatus according to the present invention, a resonance frequency is adjusted by allowing one of the power supply point and the earth point to be fixed and the other to be movable, and selecting the power supply point or the earth point which is made to be movable by a selection operation of the power supply point selection switch or the earth point switch.
The antenna apparatus according to the present invention varies the center resonance frequency for its optimization by changing a power supply point or an earth point even in case of a change in conditions for attachment to an electronic device to which the apparatus is attached, a change in environmental conditions, etc. When used for various electronic devices, the antenna apparatus can interchange data and the like under good conditions by eliminating the need for adjustment. This antenna apparatus can be also used for a so-called multiband communication device capable of compliance with various communication systems having different communication frequency bands and promote miniaturization and cost saving of the device.
The antenna apparatus according to the present invention comprises an antenna section having an antenna element provided with a power supply point and at least two or more earth points; an earth point switch means which is provided for each of the earth points and connects or disconnects each earth point from a ground; and an impedance adjustment means which is provided for the power supply point and performs impedance matching. In the antenna apparatus, a selection operation of the earth point switch means selects the earth points and adjusts a resonance frequency, and the impedance adjustment means performs optimal impedance matching corresponding to the adjusted resonance frequency.
This antenna apparatus also varies the center resonance frequency for its optimization by changing a power supply point or an earth point even in case of a change in conditions for attachment to an electronic device to which the apparatus is attached, a change in environmental conditions, etc. The antenna apparatus can interchange data and the like under good conditions by using an impedance adjustment means for optimal impedance matching. Even when a low-cost substrate is used, this antenna apparatus can implement miniaturization and provide optimal impedance matching. The antenna apparatus can be used for a so-called multiband communication device capable of compliance with various communication systems having different communication frequency bands and promote miniaturization and cost saving of the communication device itself. Further, the antenna apparatus according to the present invention can be attached to various electronic devices and configure a small, light-weight, and user-friendly wireless communication module for providing an excellent communication function in addition to a storage function and a wireless communication function.
The foregoing and other advantages and features of the present invention will become more apparent from the detailed description of the preferred embodiments of the invention given below with reference to the accompanying drawings.